By Nicole Brodzik
They’ll attach to just about anything they can get a grip on and they don’t care who it hurts – whether that’s a boat, a child’s foot or the entire food chain. Zebra mussels have been a part of the Lake Minnetonka ecosystem since 2010. The small mussel is named for it’s striped outer shell and since its introduction to Lake Minnetonka seven years ago, it’s taken a toll on native populations.
According to Eric Fieldseth from the Minnehaha Creek Watershed District, the tiny mollusk has killed off all the native mussels in Lake Minnetonka. Fieldseth and researchers from the Minnesota Aquatic Invasive Species Research Center are working on method to stop the same thing from happening elsewhere, and it all starts with the microscopic, baby mussels.
“When you look at them in the lab they just kind of flutter around,” said Michael McCartney, a zebra mussel expert at the research center. “They really are beautiful little animals.”
But to McCartney, they’re even more beautiful dead. Veligers are the infant stage of zebra mussels. They spend about two to three weeks floating through the water before they anchor to an object and grow into adult mussels.
According to McCartney, these veligers could be the key to controlling the species’ spread. He, his staff and his students have spent hours hovering over microscopes checking to see if the tiny, beautiful creatures have died yet. They spent last year working on a copper-compound that they are now using in the western bays of Lake Minnetonka to attempt to kill the mussels before they mature.
“They have these little cilia that flutter and move,” McCartney said. “If they are swimming or moving, or if we can see the gut moving or the heart beating, we know we didn’t succeed.”
McCartney and the research center staff members are currently working with the watershed district on the study in Lake Minnetonka. While they say it’s nearly impossible to eradicate the zebra mussel population from the lake, they hope to develop a solution for newly infested lakes.
“We think of it as using the lake as our bigger lab,” McCartney said. “We can’t eradicate them here. There’s too much effort required to bring down populations here enough to reintroduce native mussels and it’s very cost restrictive. But we’re hoping these techniques can be used on new infestations so other lakes don’t get as bad as this one.”
Zebra mussels are filter feeders and therefore eat all the micro organisms that help other marine populations survive. Without the nutrients necessary to support life, the lake water is clear.
“They really mess up the food chain,” said Eric Evenson, Lake Minnetonka Association executive director. “They eat the micro organisms and then the larger animals, like walleye, don’t have food and those populations are down all over the state. It’s something we have to figure out.”
But not everyone is happy with what happens after the invaders are gone and native populations of plants and animals are on the rebound. According to McCartney’s coworker Peter Sorenson, getting rid of invasive species can be a controversial topic.
“People will get upset then because they can’t use the lakes as easily for recreation,” Sorenson said. “They don’t understand or appreciate what the lakes could and should look like.”
Evenson said he’s heard the argument that because zebra mussels have made their way into Lake Minnetonka, there’s no point in continuing boat inspections.
“People will say, well they’re already here,” he said. “So, yes, we lost that battle. But there’s so much more we have to think about.”
McCartney also said that abandoning inspections is far from the right decision, as zebra mussels are only found in about 115 of Minnesota’s nearly 12,000 lakes. Without inspection, the mussels are much more likely to spread beyond the shores of Lake Minnetonka, Lake Waconia, Lake Minnewashta and Independence Lake.
What to look for next
Zebra mussels aren’t the only invader the Department of Natural Resources, the watershed district, lake association and research center are working to keep out of local waterways. Spiny water flea and the parasite heterosporosis are also concerning for researchers.
“People doing inspections are keeping eye out for these new invaders,” McCartney said. “There’s reasonable hope that general knowledge and vigilance is the key to stopping the spread of these invaders. If we had spiny water flea here on Lake Minnetonka, that would be a huge problem.”
Spiny water flea is a type of microscopic plankton that eats other zooplankton and disrupts the food chain much like a zebra mussel. These tiny organisms are even easier to transport as they are often caught up on fishing lines and are easily transported in bilge or bait water. They are currently not found in any bodies of water in the metro area, but have found their way from the Great Lakes into Mille Lacs and Lake of the Woods.
Heterosporosis is a parasite that infects fish by planting spores inside the muscle tissue of the fish, which eventually rupture the tissues and liquefy the muscle.
“They basically become swimming sacks of parasites,” Evenson said.
The disease is transmitted through spores floating in the water or infected fish being consumed, which means any kind of ballast, bilge or bait water can easily spread the parasite from lake to lake. Evenson said it’s more important than ever that people are cleaning their boats and letting the boats dry completely so as not to infect new bodies of water, which means 27 days on dry land between launches.
Heterosporosis is beginning to take a toll on the economy, according to the DNR, as it easily infects species like walleye and yellow perch. It’s been found in 26 lakes in Minnesota, but Evenson said that he’s not convinced the current economic impact the parasite is having will make a difference.
“It has short-term effect on economy and then get used to it being there,” he said. “That’s what happened with carp, Eurasian milfoil and it will happen with zebra mussels and any other invaders. We’ll adapt. People don’t seem to care after it stops effecting their bottom line.”
But it’s not all bad news. With studies like the one being done in Lake Minnetonka, researchers are hopeful that invasive prevention and local elimination is possible. Sorenson said he hopes that with the help of responsible river and lake goers, Minnesota’s waterways can be saved for future generations.
“Invasives are a reflection of the whole issue. It’s about climate change and people’s movement,” he said. “It’s not too late, but it’s getting late.”
Follow Nicole Brodzik on Facebook at facebook.com/mnsunsailor.